BLOOD MEDIA 43 



in the proportion of about 5 drops to 5 c.c. of agar ; the blood 

 is added to the melted agar as in Wertheim's medium. 

 W. B. M. Martin recommends the substitution of sodium 

 phosphate ('5 per cent.) for sodium chloride in the preparation 

 of the agar, and uses fluid human serum sterilised at 57 C. in 

 place of blood. He also finds that the same agar medium 

 allowed to solidify and then smeared on the surface with a drop 

 or two of human serum gives excellent results. 



Any of these media may be used for plate cultures, the agar 

 being melted and cooled to 40 C. as for agar plates ; the serum 

 or blood is then added ; the mixture is inoculated in the usual 

 way and poured out in Petri dishes. 



"Nasgar." This is a serum medium introduced by Gordon for the 

 isolation of the meningococcus. It is prepared as follows : 

 Ascitic fluid . . . . . . 15 c.c. 



Distilled water 35 c.c. 



Nutrose 1 ...... 1 gramme. 



Put in a flask, bring to boil, constantly shaking till ebullition occurs ; 

 filter. Of the resultant fluid take one part and add two parts of ordinary 

 peptone agar. Steam for half an hour and place in tubes. 



Blood Media. 



Blood-Smeared Agar. This medium was introduced by 

 PfeifTer for growing the influenza bacillus, and it has been used 

 for the organisms which do not readily grow on the ordinary 

 media, e.g., the gonococcus and the pneumococcus. Human 

 blood or the blood of animals may be used. " Sloped tubes " 

 (vide p. 53) of agar are employed (glycerin agar is not so 

 suitable). Purify a finger first with 1-1000 corrosive sublimate, 

 dry, and then wash with absolute alcohol to remove the sub- 

 limate. Allow the alcohol to evaporate. Prick with a needle 

 sterilised by heat, and, catching a drop of blood in the loop of a 

 sterile platinum wire (vide p. 55), smear it on the surface of the 

 agar. The excess of the blood runs down and leaves a film 

 on the surface. Cover the tubes with indiarubber caps, and 

 incubate them for one or two days at 37 C. before use, to 

 make certain that they are sterile. Agar poured out in a thin 

 layer in a Petri dish may be smeared with blood in the same 

 way and used for cultures. 



Serum Agar is prepared in a similar way by smearing the 

 surface of the agar with blood serum, or by adding a few drops 

 of serum to the tube and then allowing it to flow over the 

 surface. 



1 Nutrose is an alkaline preparation of casein. 



